Simulation of swelling of model polymeric gels by subcritical and supercritical solvents

Monte Carlo simulations have been performed to examine the volumetric behav ior of model nonionic gel systems where the solvent is at subcritical and s upercritical conditions. It is found that the degree of swelling correlates well with the density changes of the solvent: swelling decreases as the so lvent becomes less dense. As the temperature is increased at constant press ure, gel swelling exhibits a monotonic decreasing trend whose onset approxi mately agrees with the solvent's boiling point for subcritical pressures an d, for supercritical pressure, with the location of the lower critical solu tion temperature (LCST) of the solvent-uncrosslinked polymer system. Eviden ce of an incipient first-order volume phase transition has been detected fo r polymeric networks with long strand lengths in contact with a supercritic al solvent. (C) 1999 American Institute of Physics. [S0021-9606(98)51448-1] .